Update notifications to be compliant with next phpBB release

This PR has changes that will make Board Rules work with the next phpBB release.

The notification type names must now match the service name for the notifications. In addition to that, we can now use a service name that follows the policy guidelines of prefixing it with vendor.extension.

Also, to prevent board failures, when phpBB is updated to RC4 (or whatever is next) they disable any non-core notification types, so we also have to re-enable ours while changing the name in the migration.

DO NOT MERGE UNTIL WE KNOW WHAT THE NEXT RELEASE VERSION OF PHPBB IS